Implantable medical devices may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, or gastroparesis. An implantable medical device may deliver electrical stimulation therapy via leads that include electrodes located proximate to the spinal cord, pelvic nerves, stomach, or within the brain of a patient. In general, the implantable medical device delivers electrical stimulation therapy in the form of electrical pulses.
A clinician may select values for a number of programmable therapy parameters in order to define the electrical stimulation therapy to be delivered to a patient. For example, the clinician may select an amplitude, which may be a current or voltage amplitude, and pulse width for a stimulation waveform to be delivered to the patient, as well as a rate at which the pulses are to be delivered to the patient. The clinician may also select as parameters particular electrodes within an array of electrodes located on, for example, one or two implanted leads, to be used to deliver the pulses, as well as the polarities of the selected electrodes. A group of parameter values may be referred to as a program in the sense that they drive the electrical stimulation therapy to be delivered to the patient.
The process of selecting values for the parameters that provide adequate results can be time consuming, and may require a great deal of trial and error before a “best” program is discovered. The “best” program may be a program that is better in terms of clinical efficacy (e.g., symptom relief, coverage area) versus side effects experienced and medical device performance characteristics (e.g., power consumption) than other programs tested. As a portion of the overall parameter selection process, the process of selecting electrodes and the polarities of the electrodes, e.g., the process of selecting electrode combinations, can be particularly time-consuming and tedious. The clinician may need to test all possible combinations of electrodes within the set implanted in the patient, or a significant portion thereof, in order to identify a “best” combination of electrodes and their polarities.
In some cases, the clinician may test combinations by manually specifying each combination to test based on intuition or some idiosyncratic methodology, and recording notes on the efficacy and side effects of each combination after delivery of stimulation via that combination. In this manner, the clinician is able to later compare and select from the tested combinations. As an example illustrating the magnitude of such a task, implantable medical devices commonly deliver spinal cord stimulation therapy (SCS) to a patient via two leads that include eight electrodes per lead and provide well over one million potential electrode combinations.
Prior to implanting an implantable medical device, a trial stimulator may be used to deliver stimulation, e.g., SCS, to the patient during a trial (or trialing) period. The trial stimulator may be an external stimulator coupled to one or more percutaneously implanted leads. The result of the trial period is a general indication as to whether stimulation will be an efficacious therapy for the patient. Based on the trial period, a decision as to whether to implant an implantable medical device and leads for chronic delivery of stimulation may be made. The lengthy trial and error process of selecting electrode combinations occurs not only prior to implanting the implantable medical device and leads, but may also occur periodically for the life of the therapy. For example, the lengthy trial and error process of selecting electrode combinations occurs only after implanting the implantable medical device and leads.